Unable to change number of vertices after adding a bezier circle in blender 2.83
You have added a curve circle, instead of a mesh circle. A curve circle does not have vertices, it has control points, but these cannot be adjusted when adding the object. A mesh circle will have the option to adjust the number of vertices.
Press Shift+A&gt; Mesh&gt; Circle to add a mesh circle. Then the Adjust Last Operation panel (the panel in the bottom left) will show the option to adjust the vertices.